The present invention relates to a magnetic head structure used in a magnetic disk apparatus.
A magnetic disk apparatus includes a plurality of disks and a plurality of magnetic head structures inserted between the disks. The magnetic head structure is provided in a magnetic head slider. The surface of the magnetic head slider facing the disk is called a floating surface. The magnetic head structure comprises a coil, a magnetic pole allowing a magnetic flux generated by the coil to transmit therethrough and forming a magnetic gap, an insulating layer surrounding the coil, and a protective film covering the insulating layer and the magnetic pole, with these members being provided on a substrate forming the magnetic head slider. Due to the magnetic gap, data can be written into the disk. Further, a shield and a reading element (MR element) are arranged on the substrate.
When data are written into the disk, an electric current is supplied to the coil. The electric current flowing through the coil generates a magnetic flux, and the magnetic flux leaking in the magnetic cap of the magnetic pole writes data into the disk. On the other hand, when data are read from the disk, data are read by the MR element. Recently, the quantity of floating of the magnetic head slider has been reduced in order to increase the recording density and, for example, the quantity of floating has been reduced to equal to or less than 10 nm.
In the magnetic head structure, the substrate is made of Al2O3—TiC, the coil is made of copper, the magnetic pole and the shield are made of a magnetic material such as NiFe, the protective film is made of alumina, and the insulating layer is made of a resin material such as a photoresist. In this manner, the whole magnetic head structure is covered with a protective film made of alumina, and the coil and the insulating layer, which have coefficients of thermal expansion different from that of the protective film, are arranged within the magnetic head structure.
The coefficient of thermal expansion of alumina is 5.8×10−6, the coefficient of thermal expansion of copper is 17.2×10−6, the coefficient of thermal expansion of Permalloy, which is a magnetic material, is 10×10−6, and the coefficient of thermal expansion of photoresist is 30-70×10−6. The coefficient of thermal expansion of copper or magnetic material is approximately two or three times greater than that of alumina. The coefficient of thermal expansion of photoresist is approximately 10 times greater than that of alumina.
When the temperature of the interior in the magnetic disk apparatus rises or when the temperature rises due to the supply of an electric current, a thermal deformation may occur in the magnetic head structure due to the difference in coefficient of thermal expansion of the constituent materials of the magnetic head structure. Such a thermal deformation may cause deformation of the floating surface.
An observation of the deformation in the floating surface reveals a considerable expansion of the insulating layer comprising a photoresist having a great coefficient of thermal expansion and the shield layer comprising a magnetic material and due to this, an unwanted phenomenon, that a portion of the floating surface near the magnetic pole protrudes toward the disk, occurs. If a deformation in the floating surface occurs, the minimum quantity of floating of the magnetic head slider is substantially reduced, and there arises the possibility that a portion of the floating surface near the magnetic pole comes into contact with the disk and reliability may be reduced.
Therefore, it is desirable to reduce the protrusion, of the portion of the floating surface near the magnetic pole, toward the disk.
Conventionally, there is a proposal to reduce the protrusion of the portion of the floating surface near the magnetic pole by changing the materials of the insulating layer and the protective film. For example, in Japanese Unexamined Patent Publication (Kokai) No. 2000-306213, it is proposed that the protective film is divided into two portions, and a material having a higher Young's modulus is used in the portion nearer to the floating surface and a material having a lower Young's modulus is used in the portion more distant from the floating surface. Also, in Japanese Unexamined Patent Publication (Kokai) No. 2000-306215, it is proposed to use a resin having a low glass transition point for the insulating layer. However, as there is a large difference between the coefficient of thermal expansion of the protective film and that of the insulating layer, as described above, and as the shield is also one of the factors in the deformation, the problem of the thermal deformation cannot be fundamentally solved even if a difference between the coefficient of thermal expansion of the protective film and that of the insulating layer is slightly reduced.